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Sunday, November 24, 2024

Nanopasta, no, really

Fig. 1 from the linked paper
Here
is a light-hearted bit of research that touches on some fun physics.  As you might readily imagine, there is a good deal of interdisciplinary and industrial interest in wanting to create fine fibers out of solution-based materials.  One approach, which has historical roots that go back even two hundred years before this 1887 paper, is electrospinning.  Take a material of interest, dissolve it in a solvent, and feed a drop of that solution onto the tip of an extremely sharp metal needle.  Then apply a big voltage (say a few to tens of kV) between that tip and a nearby grounded substrate.  If the solution has some amount of conductivity, the liquid will form a cone on the tip, and at sufficiently large voltages and small target distances, the droplet will be come unstable and form a jet off into the tip-target space.  With the right range of fluid properties (viscosity, conductivity, density, concentration) and the right evaporation rate for the solvent, the result is a continuously forming, drying fiber that flows off the end of the tip.  A further instability amplifies any curves in the fiber path, so that you get a spiraling fiber spinning off onto the substrate.   There are many uses for such fibers, which can be very thin.

The authors of the paper in question wanted to make fibers from starch, which is nicely biocompatible for medical applications.  So, starting from wheat flour and formic acid, they worked out viable parameters and were able to electrospin fibers of wheat starch (including some gluten - sorry, for those of you with gluten intolerances) into nanofibers 300-400 nm in diameter.  The underlying material is amorphous (so, no appreciable starch crystallization).  The authors had fun with this and called the result "nanopasta", but it may actually be useful for certain applications.


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